The present invention relates to a light-sensitive photoresist composition and a process for producing such a composition. In particular, the subject invention relates to a photoresist composition comprising: a composition comprising: a) a novolak resin partially esterified with from about 3 to about 7 weight percent of a naphthoquinonediazidosulfonyl group; b) one or more dilution resins; and c) at least one solvent. Such a photoresist composition provides a positive photoresist that exhibits low absorption for thicker films, good photospeed, adjustable contrast, good shelf life stability, low outgassing potential, substantially no crystallization, excellent coating properties and broadband sensitivity.
Photoresist compositions are used in microlithography processes for making miniaturized electronic components, such as in the fabrication of computer chips and integrated circuits. Generally, in these processes, a thin coating of a film of a photoresist composition is first applied to a substrate material, such as silicon wafers used for making integrated circuits. The coated substrate is then baked to evaporate any solvent in the photoresist composition and to fix the coating onto the substrate. The baked-coated surface of the substrate is next subjected to an image-wise exposure to radiation.
This radiation exposure causes a chemical transformation in the exposed areas of the coated surface. Visible light, ultraviolet (UV) light, electron beam and X-ray radiant energy are radiation types commonly used today in microlithographic processes. After this image-wise exposure, the coated substrate is treated with a developer solution to dissolve and remove either the radiation-exposed (in the case of positive photoresist) or the unexposed (in the case of negative photoresist) areas of the coated surface of the substrate.
There are two types of photoresist compositions, negative-working and positive-working. When negative-working photoresist compositions are exposed image-wise to radiation, the areas of the resist composition exposed to the radiation become less soluble to a developer solution (e.g. a cross-linking reaction occurs) while the unexposed areas of the photoresist coating remain relatively soluble to such a solution. Thus, treatment of an exposed negative-working resist with a developer causes removal of the non-exposed areas of the photoresist coating and the creation of a negative image in the coating thereby uncovering a desired portion of the underlying substrate surface on which the photoresist composition was deposited.
On the other hand, when positive-working photoresist compositions are exposed image-wise to radiation, those areas of the photoresist composition exposed to the radiation become more soluble to the developer solution (e.g. a rearrangement reaction occurs) while those areas not exposed remain relatively insoluble to the developer solution. Thus, treatment of an exposed positive-working photoresist with the developer causes removal of the exposed areas of the coating and the creation of a positive image in the photoresist coating.
Again, a desired portion of the underlying substrate surface is uncovered. After this development operation, the now partially unprotected substrate may be treated with a substrate-etchant solution or plasma gases and the like. The etchant solution or plasma gases etch that portion of the substrate where the photoresist coating was removed during development. The areas of the substrate where the photoresist coating still remains are protected and, thus, an etched pattern is created in the substrate material that corresponds to the photomask used for the image-wise exposure of the radiation. Later, the remaining areas of the photoresist coating may be removed during a stripping operation, leaving a clean etched substrate surface. In some instances, it is desirable to heat treat the remaining photoresist layer, after the development step and before the etching step, to increase its adhesion to the underlying substrate and its resistance to etching solutions.
Positive working photoresist compositions are currently favored over negative working resists because the former generally have better resolution capabilities and pattern transfer characteristics. Photoresist resolution is defined as the smallest feature that the resist composition can transfer from the photomask to the substrate with a high degree of image edge acuity after exposure and development. In many manufacturing applications today, resist resolution on the order of less than one micron is quite common. In addition, it is almost always desirable that the developed photoresist wall profiles be near vertical relative to the substrate. Such demarcations between developed and undeveloped areas of the resist coating translate into accurate pattern transfer of the mask image onto the substrate.
Efforts have been previously been made to attach DNQ groups to novolak resins. However, these efforts have been directed toward providing a resin that functions as both the film forming component and the photosensitizer. This enables the production of single component photoresists because it is not necessary to add a separate photoactive component to photosensitive the photoresist composition. One of the first patents relating to this technology was U.S. Pat. No. 3,046,120. An ortho-cresol/formaldehyde novolak resin was esterified with a naphthoquinone-(1,2)-diazide-(2)-5-sulfonyl chloride to provide a single component photosensitive composition that useful for the production of printing plates. Other patents that relate to these attempts to combine a photosensitive compound with a phenolic resin are U.S. Pat. Nos. 3,635,709; 4,123,279 and 4,306,011.
U.S. Pat. No. 5,178,986 relates to a light sensitive mixture useful as a positive acting photoresist. The mixture contains a compound that comprises the reaction product of a DNQ and an oligomeric phenol. More recent attempts to provide a photoresist composition comprising the esterification product of a phenolic resin and a DNQ are described in U.S. Pat. No. 5,279,918. An ortho-quinone diazide sulfonyl chloride was condensed with a relatively low molecular weight novolak resin, wherein from 40% to 90% of the phenolic hydroxy groups were condensed with the DNQ groups. This provided a high concentration of DNQ moieties on the novolak resin backbone.
In U.S. Pat. No. 5,422,221 a photoresist composition is disclosed wherein the novolak resin serves as both the alkali-soluble film-forming resin and the photosensitive component of the composition. This is accomplished by replacing the hydrogen atom of a hydroxyl group in the novolak resin with a DNQ group in a proportion of 0.03 to 0.27 mol per hydrogen atom (believed to be equivalent to 3 to 27% esterification). It was disclosed that more than 0.27 mol% [sic] substitution results in a novolak resin that is less soluble in the photoresist solvent and that less than 0.03 mol% [sic] substitution provides a novolak resin that is too low in film retentivity so that the resulting photoresist composition cannot be patterned and is, therefore, useless.
U.S. Pat. No. 5,529,880 discloses a photoresist composition comprising: 1) the esterification product of a DNQ and a novolak resin having pendant phenol hydroxyl groups and 2) the esterification product of a phenol having 2 to 5 phenyl rings and at least 4 phenolic hydroxy groups with a DNQ having at least 50% of its phenol hydroxyl groups esterified with the DNQ. The esterification reaction to produce esterification product 1) is controlled so that a maximum of 20% of the phenolic hydroxy groups are esterified.
U.S. Pat. No. 5,723,254 discloses a positive acting photoresist composition containing a mixture of photoactive components. One component of the mixture is the esterification product of a DNQ with a low molecular weight phenolic resin. Another component is the esterification product of a DNQ with a low molecular weight phenol having from 1 to 3 aryl rings and from 1 to 3 hydroxyl groups. A third photoactive component that may be present is the esterification product of a DNQ with a relatively high molecular weight polyhydric polynuclear phenol.
The present invention relates to a photoresist composition that comprises a composition comprising: a) a novolak resin partially esterified with from about 3 to about 7 weight percent of a naphthoquinonediazidosulfonyl group; b) one or more dilution resins; and c) at least one solvent. alkali-soluble, film forming phenolic resin preferably having a weight average molecular weight from about 1,000 to 30,000, preferably from about 1,500 to 10,000. The DNQ used for partial esterification of the novolak resin contains quinonediazide sulfonyl groups that replace the hydrogen atom of hydroxyl groups in the novolak resin. The one or more dilution resins dilute the amount of partially esterified novolak resin in the composition to allow for better solution, viscosity, and other physical and chemical benefits in the composition and the resulting photoresist. The solvent suitable for use in present invention may be any of those well known to those skilled in the art, but preferably is a solvent or solvent blend that can be selected from 2-heptanone, either alone or in combination with anisole; ethyl lactate, either alone or in combination with n-butyl acetate or propylene glycol methyl ether; or propylene glycol methyl ether, either alone or in combination with ethyl 3-ethoxypropionate.
The invention further comprises a process of forming an image on a substrate. The substrate is coated with a film of the photoresist composition of the instant invention. The photoresist film is imagewise exposed through a mask with ultraviolet radiation and processed in accordance with those steps known to those skilled in the art.